This invention is related generally to impulse or drop-on-demand ink jet printers, and more particularly to such ink jet printers which are capable of printing bar codes.
The "965 printer" which has been marketed by Exxon Office Systems, a predecessor in interest to the assignee of the present invention, employs a plurality of chambers, with a single orifice for each chamber, and a single transducer for ejecting a droplet of ink from the single orifice of each chamber. In that printer, the orifices are slanted or inclined with respect to the scanning direction so as to provide a desired field height while, at the same time, maintaining a desired resolution. Further details relating to the 965 printer are disclosed in U.S. Pat. No. 4,567,570, which is assigned to the assignee of the present invention, and incorporated herein by reference.
U.S. Pat. No. 4,714,934, referred to above, describes an impulse ink jet apparatus comprising a plurality of side-by-side chambers extending along a line slanted with respect to the direction of scanning. Each of the chambers includes a plurality of orifices (preferably three orifices per chamber) arranged along a line extending substantially transverse to the scanning direction, and means for ejecting a plurality of droplets from the orifices of each of the chambers. In accordance with a preferred embodiment of the invention, an overall field of droplets (i.e., three droplets) ejected from each of the plurality of orifices prints a segment of a bar, and the overall field of droplets ejected from each of the other plurality of orifices prints a different segment of the bar. This feature, the patent teaches, permits a sufficient degree of vertical and horizontal resolution in order to achieve both bar code and alphanumeric printing.
One problem with the immediately above-described method and apparatus, it has been discovered through subsequent testing, is that the three ink droplets ejected from each of the plurality of orifices converge while in flight, thus creating a single large droplet which is unacceptable for printing bar codes. It has also been discovered that such convergence is not only a function of the distance between the orifices and a recording medium, but is also a factor which contributes to pixels having a smaller than desired height. Such smaller pixels result in gaps formed between the bar code segments which, in turn, result in an unacceptable bar code character. It would, therefore, be desirable to provide an improved bar code printer which does not produce bar code segments with gaps formed there between.